Prior art suspension systems for vehicles have used conventional coil springs and shock absorbers. U.S. Pat. No. 5,152,547, entitled “Dual Piston Strut,” and issued to Leo W. Davis on Oct. 6, 1992, discloses dual piston strut for use in vehicle suspensions. U.S. Pat. No. 6,389,341, entitled “Control System For A Vehicle Suspension,” and issued to Leo W. Davis on May 14, 2002, discloses an active control system for vehicle suspension.
Prior art suspension systems have been provided for motor vehicles to isolate the vehicle frame, or chassis, from impacts and vibrations resulting from vehicle wheels traversing uneven terrain. Vehicle ride characteristics have complex dynamics characterized by nonlinearities, vehicle roll and pitch, vehicle flexibility effects, varying parameters, unknown friction, deadzones and high amplitude disturbances. Excess vibration results in artificial vehicle speed limitations, reduced vehicle-frame life, biological effects on passengers and detrimental consequences to cargo. Present automobile suspension systems traditionally use passive suspension systems which can only offer a compromise between the two conflicting criteria of comfort and performance by providing spring and dampening coefficients of fixed rates. Passive suspension systems have been provided by separate coil springs and shock absorbing dampers, in which power is not input by a controlled power source to counteract impacts and vibrations resulting from traversing the rough terrain. The traditional engineering practice of designing spring and dampening functions as two separate functions has been a compromise from its inception in the late 1800s. As a result, vehicles have always been designed, styled and built around the space-weight requirements and performance limitations of traditional suspension configurations. Due to the demands of increased fuel mileage and decreased emissions, passenger and commercial vehicles are becoming lighter, which results in the differences between laden and unladen weights of the vehicles becoming so broad that traditional suspension systems are unable to span the load range effectively, causing serious degradation in performance of the vehicle ride quality, load handling and control.
To provide increased mobility and stability, independent passive suspensions have been developed which have proven their worth in improved mobility over rough courses, but high wheel travel has sacrificed improved stability. Active suspension systems provide a solution for improved stability, as well has providing improved mobility.
Active suspension systems reduce these undesirable ride characteristics by providing active, powered components which isolate the car body from tire vibrations induced by uneven terrain, to provide improved comfort, road handling performance and safety for a variety of terrains and vehicle maneuvers. In active vehicle suspension systems, actuators are provided to actively apply forces which counteract and balance forces applied to the chassis of the motor vehicle.